The present invention relates to a process for producing a sulfur sorbent composition for use in removing sulfur oxides from a stream of effluent gas and the resultant sorbent produced.
Desulfurization of effluent gas is achieved by various procedures known in the art. One known procedure is to treat the effluent gas with sorbents, such as calcium carbonate or calcium hydroxide.
Such sulfur sorbents are the subject, for example, of U.S. Pat. No. 4,424,197 to Powell et al. This patent discloses the use of CaO prepared by flash calcination of a special type of aragonite sand, thus generating a CaO product which reacts with SO.sub.2. This procedure has economic drawbacks due to the special raw material required and the necessary flash calcination procedure.
When commercial calcium carbonate or hydroxide is used, however, sulfur reactivity is generally unsatisfactory. Various approaches have been reported wherein improvement of sulfur reactivity is attempted.
Several disclosures have been made regarding the use of urea as an additive to hydrated calcium in order to remove NO .sub.x compounds from gas streams, or to simultaneously remove SO.sub.2 and NO.sub.x.
U.S. Pat. No. 4,731,233 discloses a process in which urea is incorporated into Ca(OH).sub.2 by dissolving urea into the hydration water. The '233 patent discloses that the urea additive does not harm the reactivity of the sorbent towards SO.sub.2. No particular hydration procedures are indicated in the '233 patent.
Such urea promoted sorbents, prepared conventionally, yield sorption rates up to a maximum of about 60% at molar ratios of Ca to sulfur of about 2.
Metal salts have been used as additives to try to improve the sulfur reactivity of calcium based sorbents. For example, Muzio et al presented a paper entitled "The Effectiveness Of Additives For Enhancing SO.sub.2 Removal With Calcium Based Sorbents" at the 1986 Joint Symposium on Dry SO.sub.2 and Simultaneous SO.sub.2 /NO.sub.x Control Technologies (EPRI Proceeding CS-4996, Vol. I, pp. 13-23). This paper reports that the incorporation of iron into the hydration water had no significant effect on SO.sub.2 capture.
Slaughter et al. presented a paper entitled "Enhanced Sulfur Capture By Promoted Calcium-based Sorbent" at the aforesaid 1986 Joint Symposium (EPRI Proceedings CS-4996, Vol. I, pp. 12-24). This paper indicates that the physical mixture of Fe.sub.2 O.sub.3 to Ca(OH).sub.2 had no significant enhancing effect on the sorbent reactivity toward SO.sub.2 during in-furnace sorbent injection experiments.
U.S. Pat. No. 4,191,115 discloses a method for enhancing the SO.sub.2 absorption of limestone used during a fluidized bed combustion of carbonaceous fuels. According to the '115 patent, limestone is sprayed with a mixture of iron sulfate and iron sulfite in a separate chamber before the limestone is injected into the fluidized bed combustor. The sulfation data presented in the '115 patent indicate that 3 hours are needed to obtain particle sulfation levels of 60%.
Thus, the state of the art indicates that urea yields no improved results for SO.sub.2 removal, and that iron is not an effective promoter for sulfur sorbents.
In light of the above, it can be seen that there is a need for a sulfur sorbent composition which is not costly to prepare and which does not require expensive starting materials.
It is therefore the principal object of the present invention to provide a process for preparing a sulfur sorbent composition which is effective and inexpensive to produce.
It is still a further object of the present invention to provide a process for producing a sorbent using iron and urea additives to enhance SO.sub.2 removal.
Other objects and advantages will become readily apparent to a person skilled in the art upon consideration of the following description of the invention.